#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int v[2000000],nr; //pres ca toate nr sunt prime
int main()
{
    int i,j,n;
    f>>n;
    for(i=2; i*i<=n; i++)
    {
        if(v[i]==0) //daca i e prim
            for(j=2; i*j<=n; j++) v[i*j]=1; //eliminam toti multiplii lui
    }
    for(i=2; i<=n; i++)
        if(v[i]==0) nr++;
    g<<nr;
    f.close();
    g.close();
    return 0;
}